'Hey,' Dupont said, holding up his hands, 'house rules. Members can propose any topic they like.'

'And who is proposing that we waste our time debating Intelligent Design?' Mason asked. He knew that Dupont was a staunch atheist, and assumed that any biologist would be familiar with the silly anti-evolution arguments.

'Oh,' Emerson said, 'Novak. Paul Novak, the theologian. He got here about three months ago. For his last seminar we got bogged down on whether the First Mover solution to the infinite regress should be considered a point in favor of the existence of God.'

'Don't worry David,' Dupont said, laughing. 'The other seminars are all completely rigorous. And as far as theologians go, Novak's not bad.'

'You will forgive me if I reserve judgment,' Mason said. 'But I am certainly not averse to exploring evolutionary theory. What exactly were you discussing?'

'It's called the 'vulnerable balls' problem,' Emerson said. 'You know: why would it ever be adaptive for a creature to expose its sexual organs the way human males and certain other mammals do? Why aren't the testicles carried inside the body for protection, instead of dangling in a defenseless sack?'

'And I was saying, just when you came in,' Dupont said, 'that I thought it might have something to do with keeping the sperm warmer than the rest of the body.'

'Actually,' Emerson said, 'the testicles themselves are kept cooler than the rest of the body's interior. But your suggestion, though a good one, isn't the currently accepted explanation.'

'What is it, then?' Dupont asked.

'Well,' Emerson said, 'the prevailing theory is that it acts as a signal to females. It's the same explanation as the peacock's plumage: Although it is not advantageous by itself, the fact that the males have such a handicap and yet survive indicates to potential mates that their other qualities must be superlative.'

'I have always considered that a cop-out,' Mason said. 'You can explain anything that way; even apparent weaknesses get turned into strengths, and Darwinism becomes non-falsifiable.'

'Starting to sound like Novak,' Dupont joked.

'Hold on a moment,' Emerson said, somewhat taken aback. 'Do you deny that the male's other traits must compensate for his vulnerability?'

'No I don't deny it,' Mason said, 'but the male does not simply pass on those other traits'he passes on his vulnerable balls too. So when a female sees him, all she can rationally conclude is, 'This male has managed to survive, and our offspring would have half of his genetic material.' That is precisely what she would conclude by looking at some other male, who did not have vulnerable balls and managed to survive.'

'So do you even doubt the peacock explanation?' Emerson said, with a hint of amusement in his voice. He felt quite relieved that Mason had turned out to be so ignorant in this area; the man had quite a reputation.

'That one seems more plausible,' Mason admitted, 'because it is so clearly related to a signaling mechanism. I imagine one could come up with a reasonable model in which the superior males efficiently invest some of their resources in plumage, because it's easier for females to distinguish bright from lackluster feathers than it is to monitor a male's ability to evade predators. In this respect, it is analogous to a human female being attracted to the big spender at a cocktail party. What I am objecting to is the knee-jerk invocation of sexual selection whenever we find an apparent handicap in nature.'

'And what is your explanation for vulnerable balls?' Emerson asked.

'Let me think a moment,' Mason said.

Dupont and Emerson sipped from their tea'now lukewarm'while Mason stared into space.

'You will think me a hypocrite,' Mason said, 'because I have come up with a sexual selection answer myself. But since we are dealing with sexual organs, I think it's appropriate.'

'Fine,' Emerson said, amused. 'So what's your theory?'

'I wonder,' Mason said, 'if it might have something to do with the fact that the testicles are the one weak spot of a human male. In other words, it's not merely that exposed testicles make the male worse in an absolute sense; but it also is the only thing that gives the female a chance in a physical confrontation. So perhaps the female is attracted to a male with 'vulnerable balls' because she knows she can discontinue future copulation if she wishes, whereas this would be almost impossible against a male with protected testicles.'

'David,' he said, 'you won't believe it until you meet them. And I won't talk further about it'you'll see for yourself. But I suppose it wouldn't hurt to tell you one thing, to give you time to prepare.'

'What's that?' Mason asked.

'After meeting Nicodemus, you will see Ludwig''

'Ludwig?' Mason asked in surprise.

'Yes, I think his parents were fans of Wittgenstein,' Dupont explained. 'Ludwig is by far the smartest of the lot. His DNA was based on samples from Einstein's brain and a few others. Anyway, you get to ask him one question.'

'What do you mean?' Mason said.

'I mean,' Dupont said, unable to restrain a large grin, 'that after you chit-chat with Nicodemus, you get to ask Ludwig any one question.'

Try as he might, Mason couldn't avoid feeling a chill run down his spine. He noticed that his arms were flush with goosebumps.

'What did you ask him?' Mason asked softly.

'I'm a philosopher,' Dupont said. 'I asked him, 'Why?''

Excellent, Mason thought. Thus far, the two best answers he had heard to this most famous of questions were, 'Because,' and 'Why not?'

'What did he say?' Mason asked, even more softly.

''Why?'' Dupont answered.

Mason paused. Did Dupont honestly not understand why Mason would want to know . . . or was that the jeneer's answer?

Dupont smiled.

'I imagine you're going through the same thought process that I did when he said that to me. But believe me, David, his answer was the best I could've received. It will keep my puny little mind busy for the rest of my days here. Because if you try to answer it'if you try to explain why it is that you want to know, 'Why?', then you start to come up with a pretty good answer to your original question.'